Hydrocarbon fuel composition and the method of operating a jet engine therewith



tates atent 2,8b7fi8l iatented Jan. 6, 1959 H'YDRDCARBON FUEL COMPOSITION AND THE METHOD 8F OPERATING A JET ENGINE THEREWITH Eiis'worth E.-Kirnrnel,'PittsburgmPa assignor to Koppers Company, linc., a corporation of Delaware No Drawing. Application June 7, 1956 Serial No. 589,861

19 Claims. cr ss-45.4

This. invention relates to power plants of the type known as jet engines, their operation and hydrocarbon fuel compositions therefor. More particularly this invention relates to improved hydrocarbon fuel compositions for jet engines and the improved method of operation resulting therefrom. In one of its more specific aspects the invention relates to improved fuels for ram jet en gines.

Currently there are three types of jet engines falling into categories known as turbo jets, ram jets, and pulse jets. The leastcomplicated of these power plants is the ram jet engine. While it is similar in operation to the turbo jet with respect to its working cycle, the two engines differ in compression steps. "Whereas compression for the turbo jet engine is provided by a gas turbine driven compressor which provides a stream of air to the combustion chamber at a desired controlled .velocity, air iiow through the combustion chamber of the ram jet engine is controlled only by the speed ofthe ram jet engine moving through-the air. Compression :for the ram jet engine is produced by the ramming effect of .the oncoming air.

Heretofore operational difficulties encountered with jet engines were believed to be primarily due to engine design and the greatest effort wastexerted in the development of better designs for jet engines capable of overcoming these difficulties. More recently, however, it has been found that not all hydrocarbons have the same characteristics when used as fuels in jet engines and that they differ in their burning characteristics sufficiently to cause notable differences in operation of jet engines.

.One of the principal objectives in thedevelopment of ram jet engines is to provide a design which develops sufiicient; thrust to extend the present level to flight speed. Other important objectives are better fuel utilization, efficiency of fuel utilization being a function of speed of flight, and motor weight reduction. The thermal efficiency of ram jet engines operating at current flight levels is approximately 40%. Lower ignition temperatures and extended fuel to air ratio limits are to a great extent properties required in a fuel to reach these objectives.

One of the primary objects of this invention is to provide a fuel capable of developing a higher percentage increase in thermal efiiciency at present flight speed levels and greater thrust for a given motor design.

Another important object of this invention is to provide hydrocarbon fuel compositions for jet engines having lower ignition temperatures.

Still another object of this invention is to provide a fuel capable of use under extended fuel to air ratio limits and having higher heats of combustion than fuels now avail able.

A still further object is to provide a new and novel igniter for hydrocarbon fuels and a new method of ignition.

The overall search for fuel compositions capable of giving the optimum in engine operation has centered about additives whose properties in the combustion processgive (111) high. heat of, combustion, (2) highflame .speed and;having (3) high density, (4) .low-toxicityand (5) low volatility.

Unexpectedly, it now has been-found-that hydrocarbon fuel compositions eminently suitable for jet engines having certain of the most highly desired characteristics are made possible by utilization of the novel additives of this invention. Broadly speaking, in one aspect, invention resides in novel hydrocarbon fuel compositions containing as additives varying percentages of certain aluminum compounds more commonly known as aluminum alkyls. These compounds may be represented by the formula (R),,Alll wherein R is ahydrocarbon radical and n is an integer of 1, 2 or 3.

Illustrative, but not-limitative, of the aluminum alkyl additives which maybe employed to advantage in the fuel compositions of this invention are trimethyl aluminum, dimethyl aluminum hydride, methyl aluminum dihydride, triethyl aluminum, diethyl aluminum hydride, ethyl aluminum dihydride, tributyl aluminum, dibutyl aluminum hydride, butyl aluminum dihydride, tri-isobutyl aluminum, di-isobutyl aluminum, isobutyl aluminum dihydride, and higher homologous aluminum alkyls andtheir hydrides.

In another embodiment of this invention it has been found that the additives above-described are very useful as igniters for hydrocarbon fuels, particularly in jet engine operation. When used in-this manner, a small quantity of the aluminum alkyl is injected into the combustion such as conventional petroleum hydrocarbon jet engine fuels including kerosene and aviation gasoline. Generally hydrocarbon fractions which may be employed boil in the range of 200 to700 F. A preferred fuel in accordance with this invention comprises a hydrocarbon fraction boiling in the range of 250 to 600 F. and containing the above-designated portions of an aluminum alkyl.

The fuels disclosed herein can be used in continuous type jet engines of the class known as turbo jet, ram jet, and pulse jet in which an atomizing type system for supplying fuel to the combustion chamber of the engine is employed. Generally these engines are operated by injecting the fuel and air into the combustion chamber of a jet engine in certain predetermined fuel-air ratios and igniting the fuel so as to heat the air and combustion gases, thus increasing the volume of gas mass which is exhausted through the exhaust zone of the jet engine. The exit of the gas mass from the rearwardly extending exhaust duct or jet nozzle is at a velocity higher than the 'fiying speed of the engine. The thrust produced thereby equals the gas mass flowing through the exhaust duct times its increase in speed, according to the law of momentum.

In order to illustrate the advantages inherent in the hydrocarbon fuel compositions of this invention certain tests were performed to illustrate the temperatures at which the fuel compositions would ignite spontaneously in air and to illustrate the upper and lower limits of the fuel to air ratio outside of which combustion could no 0 longer be supported. The point at which combustion J P4 Q. 10% tri-isobutyl aluminum in 1P4 i incombustion tests.

. flame went out. sults of the combustion vtests. V

performed on hydrocarbons having no additive for the purpose of showing the advantages in the claimed com-.

IGNITION TESTS Example I Ignition tests were performed on a gasoline having the designation JP4 with no additive and on a 10% blend of tri-isobutyl aluminum in JP4. -In the ignition tests, air

was blown into a section ofpipe-approximately 8 feet long having an inside diameter of 14 inches. Gasoline was fed to this section of pipe at a controlled flow rate and burned in the air stream to preheat it. The air stream temperature was controlled by the quantity of gasoline burned in the air stream. Hot gases from the preheating section were passed through another section of pipe of the same length and diameter and then into a 4 foot section of pipe of the same diameter fitted with a multiplicity-of nozzles for injecting fuel. distributed throughout a 6 inch length of this section. Contiguous to this section over a distance of about 1 foot the pipe was reduced from a 14 inch diameter to a 6 inch rectangular section having a single nozzle for the injec-. tion of fuel in ignition tests. From this section the gases were passed into another section of 14 inches inside diameter and then to the cooling section. The temperature of the air stream was gradually raised untilignition occurred. Evidence of ignition was a blue flame at the injection nozzle, The following results were obtained:

Fuel Ignition temperature Failed to ignite at 1,800 F. 800l,000 F. a

The foregoing is clear evidence of a substantial improvement in ignition conditions as a direct result of employing the additives of the invention. More specifically,

the decrease in ignition temperature is of the order of 800.

to 1000 F. a

Substitution of blends having" to 30% by weight of a several of the aluminum alkyls listed above, for example triethylaluminum, di-isobutyl aluminum monohydride and diethyl aluminum hydride gives ignition temperatures substantially lower than 1800 F. From these representative results it will be obvious to those skilled in the art that other aluminum alkyls and their hydrides can'be used to advantage to lower hydrocarbon ignition tem- Triethyl aluminum, diethyl aluminum monohydride, tri-isobutyl aluminum and di-isobutyl aluminum peratures.

monohydride have been found very effective for this purpose.

COMBUSTION TESTS Example II fuel feed rate was decreased over a period. of to 15 seconds until the flame went out. To determine the rich limit, the fuel feed rate was gradually increased until the In thefollowing table. are given the re- The nozzles were uniformly In the foregoing combustion tests the fuel flows given are those flows at which the flame blew out. Each value given is theaverage of 3 to 4 determinations.

In additional combustion tests, 10 and blends of triethyl aluminum in JP4 were tested in a 2 inch diameter, fuel atomizing type combustion chamber. In each case the blends burned under conditions where J P4 went out. V v

The foregoing ignition and combustion test results make it clear that substantially lower ignition temperatures are exhibited by the fuel compositions of the invention than the same fuel without additive, and that the low ignition temperature is also indicative of superior combustion properties.

While an air velocity of 200 feet per second was employed, further tests have shown that a higher air velocity of 500 to 600'feet per second gives even superior results.

The foregoing also clearly illustrates that by using alkyl aluminums in hydrocarbon fuels in accordance with this invention, extension of the rich fuel ratio is obtained which is equivalent to obtaining greater thrust for a given motor design. The amount of thrust is proportional to the quantity of fuel that can be consumed per unit of time. Extension of the upper level of fuel ratio, without flame blow out results in greater thrust. Similarly, it would be anticipated that for a given motor, additionof I aluminum alkyls to the hydrocarbon would permit higher 'other aspect of this invention, are'very useful for initial altitude flight limits as a result of extension of the rich fuel ratio.

As mentioned previously, the aluminum alkyls, in anj or start-up ignition or for reigniting following blow out. Whereas ignition times in the neighborhood of 20 milliseconds is considered excellent, each of the aluminum alkyls tested in accordance with the invention gave ignition times of the order of 10 milliseconds. Specific ones of the aluminum alkyls which have given such reduced ignition times include triethyl aluminum, triisobutyl aluminum, diethyl aluminum hydride and diisobutyl aluminum hydride. These tests were performed under normal operating conditions with a small quantity of. the ignite'r being injected into the combustion zone of an, engine containing the preheated fuel-air mixture and the ignition time recorded.

Various modifications of this invention will be apparent to those skilled in the art. It will also be obvious to those skilled in the art that alkyl aluminums other than those illustrated androf the class enumerated above and their hydrides can beemployed to advantage in this invention. Such modifications are believed to be within the spiritand scope of this invention.

I claim: a

l. The method of operating a jet engine which comprises supplying to the combustion zone of said jet engine a hydrocarbon fuel boiling in the range of 200 to 700 F. containing between 5 and 30% by weight of an aluminum compound having the formula (R),,AlH

wherein R is a lower alkyl radical and n is an integer equal to from 1 to 3, burning said fuel in the combustion zone; of said engine and exhausting resulting gases from said enginefso as to impart thrust thereto.

2. The method of claim 1 in which the aluminum alkyl is tri-isobutyl aluminum.

v 3. The method of claim l in which the aluminum alkyl is aluminum monohydride.

4. The method of claim 1 in which the aluminum alkyl is triethyl aluminum.

5. The method of claim 1 in which the aluminum alkyl is diethyl aluminum monohydride.

6. The method of claim 1 in which the aluminum alkyl is trimethyl aluminum.

7. The method of igniting a jet fuel which comprises injecting an aluminum compound having the formula (R),,AlI-I wherein R is a lower alkyl radical and n is an integer equal to from 1 to 3 into the combustion zone of a jet engine containing a normally liquid hydrocarbon boiling in the range of 200 to 700 F. and preheated to a temperature of about 800 to'1000 F.; said aluminum compound being introduced in an amount equal to from about 5% to 30% by weight of said hydrocarbon. W

8. The method of claim 7 in which the aluminum compound is tri-isobutyl aluminum.

9. The method of claim 7 in which the aluminum compound is di-isobutyl aluminum monohydride.

10. The method of claim 7 in which the aluminum compound is triethyl aluminum.

11. The method of claim 7 in which the aluminum compound is diethyl aluminum monohydride.

12. The method of claim 7 in which the aluminum compound is trimethyl aluminum.

13. A jet engine fuel consisting essentially of a normally liquid hydrocarbon boiling in the range of 200 to 700 F. and about 5% to 30% by weight of an aluminum compound having the formula (R),,AlH wherein R is a lower alkyl radical and n is an integer equal to from 1 to 3.

14. The jet engine fuel of claim 13 in which the aluminum alkyl is tri-isobutyl aluminum.

15. The jet engine fuel of claim 13 in which the aluminum alkyl is di-isobutyl aluminum monohydride.

1.6. The jet engine fuel of claim 13 in which the aluminum alkyl is triethyl aluminum.

17. The jet engine fuel of claim 13 in which the aluminum alkyl is diethyl aluminum monohydride.

18. The jet engine fuel of claim 13 in which the aluminum alkyl is trimethyl aluminum.

19. The method of operating a ram jet engine which comprises supplying to the combustion zone thereof a hydrocarbon fuel igniting in the range of about 800 to 1000 F. and boiling in the range of 250 to 600 F. containing between about 5% and 10% by weight of an aluminum compound having the formula: (R),,AlH wherein R is a lower alkyl radical and n is an integer of at least one and not more than three, burning said fuel in the combustion zone of said jet engine and exhausting the resulting gases from said engine so as to impart thrust thereto.

References Cited in the file of this patent UNITED STATES PATENTS 2,698,510 Britton et a1. Ian. 4, 1955 2,765,329 Lindsey Oct. 2, 1956 2,775,863 Traverse Jan. 1, 1957 OTHER REFERENCES Chem. and Eng. News, vol. 26, No. 26, Sept. 27, 1948, pp. 2892-3. 

1. THE METHOD OF OPERATING A JET ENGINE WHICH COMPRISES SUPPLYING THE COMBUSTION ZONE OF SAID JET ENGINE A HYDROCARBON FUEL BOILING IN THE RANGE OF 200* TO 700* F. CONTAINING BETWEEN 5 AND 30% BY WEIGHT OF AN ALUMINUM COMPOUND HAVING THE FORMULA (R)NAIH3-N WHEREIN R IS A LOWER ALKYL RADICAL AND N IS AN INTERGER EQUAL TO FROM 1 TO 3, BURNING SAID FUEL IN THE COMBUSTION ZONE OF SAID ENGINE AND EXHAUSTING RESULTING GASES FROM SAID ENGINE SO AS TO IMPART THRUST THERETO. 